Over the last two decades, the integration and performance of semiconductor chips have been improved dramatically by employing advanced photolithography technologies to transmit smaller patterns from masks to silicon wafers, which facilitated the advances of modern electronic devices such as computers, mobile-phones and TVs. In the semiconductor industry, avoiding particulate contaminations is critical to enhancing the yield of products because the deposited particles on masks and wafers can cause defects of semiconductors, thus increasing manufacturing costs. Therefore, many efforts have been made to develop filtration systems including high efficiency particulate air (HEPA) and ultra-low particulate air (ULPA) filters for eliminating particulate contaminations.
However, as shorter wavelength ultraviolet (UV) light sources, such as a 248 nm KrF and 193 nm ArF excimer laser, are used in the advanced photolithography, new contamination problems have been highlighted in cleanrooms, which are known as airborne molecular contaminations (AMCs). AMCs represent a wide range of gaseous contaminants at very low concentrations, down to parts per billion (ppb, 10−9) or parts per trillion (ppt, 10−12) levels in cleanrooms. Semiconductor Equipment and Materials International (SEMI) categorizes AMCs into four groups, i.e. acids, bases, condensables and dopants by the standard, SEMI F21-95. AMCs can originate from inside and outside cleanrooms and can include wet chemicals of the semiconductor manufacturing processes, air pollutants or construction materials. Personnel working in cleanrooms are also major sources of AMCs. Even though the concentrations of AMCs are extremely low, they may lead to an undesired doping of the semiconductors. Additionally, particles or surface film can form when gaseous AMCs are exposed to the UV lights of the photolithography. These unintentionally synthesized particles cause defects and failures of optical systems and/or patterned silicon wafers. Due to the adverse effects of AMCs, monitoring and controlling of AMCs are now important issues in the semiconductor industry. Furthermore, AMCs are still not well understood, which makes them difficult to monitor and control. While the detailed processes leading to particle formation is the subject of ongoing research, it is clear that they originate from gases because they cannot be eliminated by particle filtering.
Existing work in the area of particle contamination produced by AMCs uses sophisticated and expensive analytical methods such as gas chromatography (GC), TOF-SIMS, and other methods to identify gaseous chemical species present regardless of whether these species cause particle or film deposition. These methods suffer from lack of knowledge of what contaminants will form the deposits. Attempts to discover which species are correlated with the particle formation ensue. Ultimately this could lead to understanding the chemical reactions and pathways leading to particle or film deposition, but it is a long and difficult process.
Nevertheless, only a few detection methods, such as UV fluorescence—analysis and gas-chromatography-mass spectroscopy (GC-MS), have been used to monitor AMCs in cleanrooms as per the recommendation by the international technology roadmap for semiconductors (ITRS). Although a UV fluorescence analyzer is relatively inexpensive, its detection capabilities are limited as most uses revolve around detecting sulfur-containing inorganic compounds such as sulfur dioxide (SO2). In addition, GC-MS is an off-line detection method which determines average contamination levels for long sampling time. Other gas detection and analysis methods, chemical ionization mass spectroscopy (CI-MS) or proton transfer reaction mass spectroscopy (PTR-MS) are frequently used in the field of atmospheric sciences, but they are seldom applied for detecting AMCs in cleanrooms due to their limitations such as fragmentation (CI-MS), proton affinity (PTR-MS) as well as costs. A detection method which is economical, on-line and applicable for diverse AMCs including inorganics and organics, is not available for use in cleanroom applications.
For controlling AMC levels in cleanrooms, chemical filters, which capture AMCs by adsorption, have been developed and installed in cleanrooms in addition to the particle filters. Because the adsorption efficiency depends on the porosity and specific surface area of the media, granular activated carbons (GACs) are widely used as chemical filter media. Depending on the chemical nature of AMCs (when it is known), GACs are modified by chemical treatments or coating catalysts to enhance their adsorptive performance. Sometimes, new filtration systems are designed to remove particular AMCs. For evaluating the improved performance of the modified chemical filters, reliable detection methods are also highly desired.
Methods and/or systems for detection and elimination of particles and films formed from AMCs that are more efficient and cost effective would be advantageous. Efficient and cost-effective methods and systems for detection of particles and films formed from AMCs would also be an advantageous capability.